Research has shown that despite significant rigor and intensity, some children with an autism spectrum[unreadable] disorder fail to make significant gains in response to behavioral treatment (e.g., Sherer & Schreibman,[unreadable] 2005). The behavioral characteristics of children who excel versus those that do not are not well[unreadable] understood. The biological characteristics of such treatment responders and nonresponders are completely[unreadable] unknown. In order to determine what behavioral and biological factors predict treatment responsiveness,[unreadable] consistency regarding various aspects of treatment must be provided. For all children the type of treatment,[unreadable] age at which treatment is administered, and length of treatment must be consistent. Therefore, a Treatment[unreadable] Core (TxC) has been established to implement an evidence-based treatment for toddlers with autism[unreadable] participating in the ACE projects. A specific, manualized treatment, the STAR Program (see Appendix A),[unreadable] has been chosen as the foundation for the treatment. This curriculum incorporates evidence-based[unreadable] behavioral methods, including discrete trial teaching, pivotal response training, and teaching within[unreadable] functional routines, that are of documented effectiveness. This curriculum will be adapted to accommodate[unreadable] 2-year-old children and to include additional social goals and developmental strategies. Recently, a[unreadable] developmental, social-pragmatic intervention that incorporates both developmental and naturalistic[unreadable] behavioral strategies has been examined as a parent education adjunct to the STAR curriculum. This[unreadable] program incorporates early developmental strategies such as Responsive Teaching and Floor Time/DIR,[unreadable] which encourage joint attention, social responsiveness, and engagement in children with autism. We[unreadable] believe, and preliminary data agree, that this combination of curricula and strategies will provide an effective[unreadable] and consistent treatment for children with autism.[unreadable] Overall, the Treatment Core (TxC), has two main goals: The first is to provide state-of-the art behavioral[unreadable] treatment to all participants who meet provisional criteria for autism at 2 years. In order to meet this goal,[unreadable] the TxC will ensure consistent application of treatment practices by training all study personnel in treatment[unreadable] protocol to mastery level. Additionally, the TxC will ensure fidelity of implementation of the treatment[unreadable] protocol throughout the funding period. The second goal is to provide a quantitative index of level of[unreadable] response to treatment for each at-risk toddler for use in predictive analyses in Projects 1-4. As such, the[unreadable] TxC will collect data throughout treatment to assess learning rate and speed of progress in each curriculum[unreadable] area. Finally, the TxC will establish an overall response-to-treatment profile for each study toddler in the[unreadable] domains of symptom severity, cognitive, language, and social behavior. These profiles will be used by each[unreadable] project as well as the Integrated Biostatistics and Bioinformatic Analysis Core to determine the profiles of[unreadable] treatment responders and nonresponders.[unreadable]